Thermally conductive coating compositions, methods of production and uses thereof

ABSTRACT

A thermal interface composition is described herein that includes: a) at least two siloxane-based compounds; b) at least one inorganic micro-filler material; and c) at least one thermally conductive filler material. Additionally, a method of forming a thermal interface material is disclosed herein that includes: a) providing at least two siloxane-based compounds; b) providing at least one inorganic micro-filler material; c) providing at least one thermally conductive filler material; and d) combining the at least two siloxane-based compounds, the at least one inorganic micro-filler material and the at least one thermally conductive filler material.

FIELD OF THE INVENTION

The field of the invention is thermally conductive coating compositionsand material in electronic components, semiconductor components andother related layered materials applications.

BACKGROUND

Electronic components are used in ever increasing numbers of consumerand commercial electronic products. Examples of some of these consumerand commercial products are televisions, computers, cell phones, pagers,palm-type organizers, portable radios, car stereos, or remote controls.As the demand for these consumer and commercial electronics increases,there is also a demand for those same products to become smaller, moreefficient, longer lasting and more portable for the different end-users,including subcontractors, contractors, consumers and businesses.

As a result of the smaller size and lighter weight demands in theseproducts, the components that comprise the products must also becomesmaller. Examples of some of those components that need to be reduced insize or scaled down are printed circuit, integrated circuits or wiringboards, resistors, wiring, keyboards, touch pads, and chip packaging.

When electronic components are reduced in size or scaled down, anydefects or extraneous materials present in the larger components aregoing to be exaggerated in the scaled down components and are also goingto physically and/or electrically influence other coupled components.

In order to identify and correct defects and minimize the influence ofdefects and extraneous materials in electronic components, thecomponents, the materials used and the manufacturing processes formaking those components should be broken down and analyzed. Electroniccomponents are composed, in some cases, of layers of materials, such, asmetals, polymers, metal alloys, inorganic materials or organometallicmaterials. The layers of materials are often thin (on the order of lessthan a millimeter in thickness) and can be delicate. There may also belayers of materials that comprise contaminants or other adulteratingmaterials that should be analyzed and if possible either eliminated orcontained.

Integrated circuit (IC) chips, for example, are designed to yield higher“infant mortality” results if the chips are initially defective,substandard or unreliable. Herein, infant mortality implies failure rateclimaxes at the early stage of their lifetime. A “burn-in” processnormally screens out the chips with poor reliability, where power and aseries of test signals are applied to the circuit mounted on a socket toexcise the circuit at an elevated temperature. Since failure rate of ICchips increase exponentially with temperature, the burn-in process candetect the questionable devices in as short duration as several hours.In the burn-in test, the junction temperature of the chips is desired toexceed over the normal operational temperature to accelerate thefailure. However, the temperature must be well controlled in thehigh-powered devices to avoid overheating, which may shorten the totaluse life of the chips. Temperature control is accomplished by equippingthe burn-in socket with a thermal interface material (TIM) between thetest chips and heat sink.

Some thermal interface materials, such as GELVET® manufactured byHoneywell Electronic Materials™, have a significant technical issue:contamination of the integrated circuit (IC) chips with material fromthe thermal interface material. GELVET® is a composite of short carbonfibers that are densely planted along the Z direction in a base materialthat penetrates into the fiber matrix but leaves the top surface of thefiber free of resin. (see U.S. patent application Ser. Nos. 09/103,415;09/103,416 and 09/333,564, which are commonly owned and incorporatedherein in their entirety). This composite structure inevitably producessmall amounts of loose fibers on the top surface of the structure thatcould then be easily transferred to the chip surface under the strongmechanical actuation during the burn-in process.

Suitable base materials used in GELVET®-type of applications and othersimilar applications are those materials that are compliant and yetstrong, while ideal base materials are those materials that are not onlycompliant and strong, but also can be produced with a high degree ofpurity. Silicone is one of the best available polymers identified as abase material because of its compliant property and strength. However,it is well known that a considerable amount of volatile, low molecularweight components are present inherently as a consequence of theequilibrium polymerization utilized in silicon manufacture. Typically,silicones with viscosity below 50 cSt are more than 10% volatile, whilethose with a viscosity greater than 50 cSt are 0.5-4% volatile. Aftercuring, liquid silicone monomers convert into a solid or semi-solidrubbery state polymer and the cross-linked network can then reduce themigration of liquid friction. Though a certain amount of monomers andoligomers will unavoidably escape out of the bulk base under the harshburn-in conditions, resulting in an oily organic stain on the surface ofIC chips. The contamination not only cosmetically stains the chipsurface but also degrades the chip's thermal performance afterpackaging. So-called “space-grade” silicone has the least amount of lowmolecular weight oligomers by repeatedly distillation of industrialgrade and accordingly is very expensive.

Generally though, the use of polymers in electronic devices, such ascomputers, cell phones, televisions, appliances, and radios, has gainedincreasing popularity for several reasons, including that a) electronicdevices have gotten smaller and more complex, b) individual componentsof these devices have gotten smaller and are multi-tasking, c) polymersare cheaper and easier to produce than traditional solder or interfacematerials, and d) polymers can be easily tailored to the particular needof the component in the device unlike traditional solder material.Therefore, polymers continue to be investigated as suitable basematerials and thus suitable to replace, in whole or in part, silicone.

There are several issued patents that aim to solve similar problems byusing thermal conductive coating compositions. U.S. Pat. No. 4,842,911discloses a composite thermal interface, which consists of dual layersof a compliant silicone rubber carried on either side of a porous glasscloth. The layers are filled with thermally conductive fillers. One ofthe silicone layers is pre-vulcanized, with the other being cured andbonded in place once the interface applied.

U.S. Pat. Nos. 5,950,066 and 6,197,859 to Green and Misra teach athermal conductive coating composition, which is coated on both sides ofa metal foil to form a sandwiched compilable thermal interface betweenIC device and heat sink. The composition is made of an alkyl substitutedpoly(hydro, methyl-siloxane), a flexibilizer and thermally conductivefiller. The composition is a wax-like material. U.S. Pat. No. 4,473,113disclosed a thermally conductive sheet for the application to thesurface of an electronic apparatus. The sheets is provided as having acoating on each side thereof a material which changes state from a solidto liquid within the operating temperature range of the electronicapparatus. The material may be formulated as a meltable mixture of waxand zinc oxide. These applications that comprise wax-like materials willlikely produce similar defects as silicone.

U.S. Pat. No. 6,037,695 to Weixel teaches a composite thermal interfacepad. The pad consists of a cavitied template made from the resilientmaterial, filled with pliable thermal grease or thermal putty. U.S. Pat.No. 5,060,114 disclosed a conformable, gel-like pad filled withthermally conductive filers. A thin sheet of thermally conductive metalsuch as aluminum is positioned in contact with the surface of theconformable pad for increased thermal transfer.

U.S. Pat. Nos. 5,213,868 and 5,298,791 teach a thermally conductiveinterface composite cased on a laminated acrylic pressure sensitiveadhesive tape. At least one surface of the tape is provided as havingchannels or through-holes formed for the removal of air from betweensurfaces of heat sink or devices.

U.S. Pat. No. 5,321,582 disclosed an electronic component heat sinkassembly which includes a thermally conductive laminate formed ofpolyamide which underlies a boron nitride-filled silicone layer. Thelaminate is interposed between the electronic component and the housingof the assembly.

Despite advances made in the field of thermal interface materials andcoating compositions, there is still a need in the electronic,semiconductor and layered materials industries to produce a thermalinterface material and/or a coating composition that a) has a lowthermal resistance; b) is relatively free of oil contamination; c) makesa good coating composition; and d) can make a self-assembled physicalbarrier or interface between the underlying thermal interface materialand additional components.

SUMMARY OF THE SUBJECT MATTER

A thermal interface composition is described herein that includes: a) atleast two siloxane-based compounds; b) at least one inorganicmicro-filler material; and c) at least one thermally conductive fillermaterial.

Additionally, a method of forming a thermal interface material isdisclosed herein that includes: a) providing at least two siloxane-basedcompounds; b) providing at least one inorganic micro-filler material; c)providing at least one thermally conductive filler material; and d)combining the at least two siloxane-based compounds, the at least oneinorganic micro-filler material and the at least one thermallyconductive filler material.

DETAILED DESCRIPTION

The subject matter presented herein creates a platform technology forall silicone-based thermal interface materials that may or may not beusing cheap industrial grade silicones, and specifically solves thecontamination problem for GELVET® and related products. The presentsubject matter relates generally to a thermal interface material andmore particularly to a polysiloxane coating characterized by low thermalresistance and free of oil contamination. A suitable thermal interfacematerial or component should conform to the mating surfaces (“wets” thesurface), possess a low bulk thermal resistance and possess a lowcontact resistance. Bulk thermal resistance can be expressed as afunction of the material's or component's thickness, thermalconductivity and area. Contact resistance is a measure of how well amaterial or component is able to make contact with a mating surface,layer or substrate. The thermal resistance of an interface material orcomponent can be shown as follows:Θinterface=t/kA+2Θ_(contact)  Equation 1

-   -   where        -   Θ is the thermal resistance,        -   t is the material thickness,        -   k is the thermal conductivity of the material        -   A is the area of the interface

The term “t/kA” represents the thermal resistance of the bulk materialand “2Θ_(contact)” represents the thermal contact resistance at the twosurfaces. A suitable interface material or component should have a lowbulk resistance and a low contact resistance, i.e. at the matingsurface.

Many electronic and semiconductor applications require that theinterface material or component accommodate deviations from surfaceflatness resulting from manufacturing and/or warpage of componentsbecause of coefficient of thermal expansion (CTE) mismatches.

A material with a low value for k, such as thermal grease, performs wellif the interface is thin, i.e. the “t” value is low. If the interfacethickness increases by as little as 0.002 inches, the thermalperformance can drop dramatically. Also, for such applications,differences in CTE between the mating components causes the gap toexpand and contract with each temperature or power cycle. This variationof the interface thickness can cause pumping of fluid interfacematerials (such as grease) away from the interface.

Interfaces with a larger area are more prone to deviations from surfaceplanarity as manufactured. To optimize thermal performance, theinterface material should be able to conform to non-planar surfaces,such as those found in GELVET® and similar components, and thereby lowercontact resistance.

Optimal interface materials and/or components possess a high thermalconductivity and a high mechanical compliance, e.g. will yieldelastically when force is applied. High thermal conductivity reduces thefirst term of Equation 1 while high mechanical compliance reduces thesecond term. The layered interface materials and the individualcomponents of the layered interface materials described hereinaccomplish these goals. When properly oriented, the thermally conductivefibers of the compliant fibrous interface component described hereinwill span the distance between the mating surfaces thereby allowing acontinuous high conductivity path from one surface to the other surface.If the fibers are flexible and able to move in its tip region, bettercontact can be made with the surface. This contact will result in anexcellent degree of surface contact and will minimize the contactresistance of the interface material.

As mentioned, a coating material and/or composition has been developedthat that a) has a low thermal resistance; b) is relatively free of oilcontamination; c) makes a good coating composition; and d) can make aself-assembled physical barrier or interface between the underlyingthermal interface material and additional components. Furthermore, theself-assembled physical barrier is formed inside the coatingcomposition, utilizing a micro-filler and phase separation of twosilicone based macro-monomers, which will subsequently be crosslinked toform a coating base. The composition generally comprises: a) at leasttwo siloxane-based compounds with each compound having a differentsolubility parameter, such as a substituted polysiloxane and/or analkenyl-terminated polydialkylsiloxane; b) at least one inorganicmicro-filler material; and c) at least one thermally conductive fillermaterial. Optionally, the coating composition and/or material maycomprise additives including a catalyst, an inhibitor, and/or arheological modifier. The materials and coating compositions disclosedherein creates a self-assembly physical barrier inside coatingcomposition, utilizing a micro-filler and phase separation of differentpolysiloxanes. Low thermal resistance is achieved by using combinedthermal fillers.

Additionally, a method of forming a thermal interface material isdisclosed herein that includes: a) providing at least two siloxane-basedcompounds; b) providing at least one inorganic micro-filler material; c)providing at least one thermally conductive filler material; and d)combining the at least two siloxane-based compounds, the at least oneinorganic micro-filler material and the at least one thermallyconductive filler material.

As used herein, the term “interface” means a couple or bond that formsthe common boundary between two parts of matter or space. An interfacemay comprise a physical attachment of two parts of matter or componentsor a physical attraction between two parts of matter or components,including bond forces such as covalent and ionic bonding, and non-bondforces such as Van der Waals, electrostatic, coulombic, hydrogen bondingand/or magnetic attraction.

The first contemplated component of the thermal interface materialsand/or coating composition comprises at least one siloxane-basedcompound. Any suitable siloxane-based and/or polysiloxane compounds canbe used, however, where there are more than two polysiloxane orsiloxane-based compounds incorporated, each should have differentsolubility parameters. Also, it is contemplated that if there are two ormore polysiloxane compounds present in the composition that they areincompatible and will inevitably form two separated organic micro-phaseswhen mixed. In theory, the phase separation of the two macro-monomerscooperated with the filler forms a hedge membrane on the top surface ofsilicone coating and essentially blocks the passageway of the monomersand oligomers migrating from both coating and GELVAT® bases. Thepolysiloxane compound may be substituted by a functional group or othersubstituent. In contemplated embodiments, the substituents comprise theclass of alkyl groups, aromatic groups, cage compounds and/or halidegroups. As used herein, the term “alkyl” is used herein to mean abranched or unbranched saturated hydrocarbon group of at least onecarbon atom, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, t-butyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl,tetracosyl and the like. Contemplated alkyl groups herein contain 1 to100 carbon atoms, and more contemplated alkyl groups comprise 1 to 25carbon atoms. As used herein, the term “aryl” or “aromatic” is usedherein to mean a monocyclic aromatic species of 5 to 14 carbon atoms,and typically comprises a phenyl group. Optionally, these groups aresubstituted with one to four, more preferably one to two, lower alkyl,lower alkoxy, hydroxy, and/or nitro substituents. As used herein, theterms “halogen” and “halide” are used to mean fluoro, chloro, bromo, oriodo groups or substituents, and usually relates to halogen substitutionfor a hydrogen atom in an organic compound.

As used herein, the term “monomer” refers to any chemical compound thatis capable of forming a covalent bond with itself or a chemicallydifferent compound in a repetitive manner. The repetitive bond formationbetween monomers may lead to a linear, branched, super-branched, orthree-dimensional product. Furthermore, monomers may themselves compriserepetitive building blocks, and when polymerized the polymers formedfrom such monomers are then termed “blockpolymers”. Monomers may belongto various chemical classes of molecules including organic,organometallic or inorganic molecules. The molecular weight of monomersmay vary greatly between about 40 Dalton and 20000 Dalton. However,especially when monomers comprise repetitive building blocks, thenmonomers may have even higher molecular weights. Monomers may alsoinclude additional groups, such as groups used for crosslinking.

As used herein, the term “crosslinking” refers to a process in which atleast two molecules, or tow portions of a long molecule, are joinedtogether by a chemical interaction. Such interactions may occur in manydifferent ways including formation of a covalent bond, formation ofhydrogen bonds, hydrophobic, hydrophilic, ionic or electrostaticinteraction. Furthermore, molecular interaction may also becharacterized by an at least temporary physical connection between amolecule and itself or between two or more molecules.

As still further used herein, the phrases “cage structure”, “cagemolecule”, and “cage compound” are intended to be used interchangeablyand refer to a molecule having at least eight atoms arranged such thatat least one bridge covalently connects two or more atoms of a ringsystem. In other words, a cage structure, cage molecule or cage compoundcomprises a plurality of rings formed by covalently bound atoms, whereinthe structure, molecule or compound defines a volume, such that a pointlocated within the volume cannot leave the volume without passingthrough the ring. The bridge and/or the ring system may comprise one ormore heteroatoms, and may contain aromatic, partially saturated, orunsaturated groups. Further contemplated cage structures includefullerenes, and crown ethers having at least one bridge. For example, anadamantane or diamantane is considered a cage structure, while anaphthalene or an aromatic spirocompound are not considered a cagestructure under the scope of this definition, because a naphthalene oran aromatic spirocompound do not have one, or more than one bridge.

The polysiloxane compound may also comprise at least onealkenyl-terminated polydialkylsiloxane. The term “alkenyl” is usedherein to mean a branched or a straight-chain hydrocarbon chaincontaining from 2 to 24 carbon atoms and at least one double bond.Contemplated alkenyl groups herein contain 1 to 12 carbon atoms. Inother contemplated embodiments, the alkenyl group of thealkenyl-terminated polydimethylsiloxane comprises 2 to 10 carbon atoms,and in other contemplated embodiments, the alkenyl group comprises avinyl group. The alkyl substituent that forms part of thepolydialkylsiloxane may comprise any suitable alkyl group alreadymentioned herein, and in contemplated embodiments, comprises a methylgroup, an ethyl group, a propyl group, a butyl group or a pentyl group.

Another contemplated siloxane-based compound or material of contemplatedthermal interface materials and/or coating compositions comprises atleast one hydride-functional siloxane. As used herein, the term“hydride” means an inorganic compound of hydrogen with another element.Some hydrides are covalent and others are ionic. Hydrides may either bebinary or complex; the latter are transition-metal complexes, e.g.carbonyl hydrides and cyclopentadienyl hydrides. Hawley's CondensedChemical Dictionary, Fourteenth Edition, Richard J. Lewis, Sr., JohnWiley & Sons, New York (2001). A contemplated hydride-functionalsiloxane comprises dimethylsiloxane-methylhydrosiloxane copolymer.

An additional contemplated component of thermal interface materialsand/or coating compositions comprises at least one inorganicmicro-filler or filler material. Contemplated inorganic filler materialsmay comprise silicon dioxide flakes or powder, silica powder or flakesor a combination thereof. Contemplated inorganic fillers comprise achemical composition similar to that of silicon dioxide and isexcessively blended into the coating composition. The filler ispre-coated with hexamethyldisilazane, which makes filler preferablycompatible to only one type of polysiloxane. The flake-like filler alsohas a very small particle size (<0.1 micro) and a large surface area.Dispersion of filler particles can be facilitated by addition offunctional organometallic coupling agents or “wetting” agents, such asorganosilane, organotitanate, organozirconium, etc. Organotitanate actsa wetting enhancer to reduce paste viscosity and to increase fillerloading. An organotitanate that can be used is isopropyl triisostearyltitanate. The general structure of organotitanate is RO-Ti(OXRY) whereRO is a hydrolyzable group, and X and Y are binder functional groups.

Yet another contemplated component of contemplated thermal interfacematerials and/or coating compositions comprises at least one thermallyconductive filler material. Thermal filler particles to be dispersed inthe thermal interface component or mixture should advantageously have ahigh thermal conductivity. Suitable filler materials include metals,such as silver, copper, aluminum, and alloys thereof; and othercompounds, such as boron nitride, aluminum nitride, silver coatedcopper, silver-coated aluminum, conductive polymers and carbon fibers.Combinations of boron nitride and silver or boron nitride andsilver/copper also provide enhanced thermal conductivity. Boron nitridein amounts of at least 20 wt % and silver in amounts of at least about60 wt % are particularly useful. Preferably, fillers with a thermalconductivity of greater than about 20 and most preferably at least about40 w/m° C. can be used. Optimally, it is desired to have a filler of notless than about 80 w/m° C. thermal conductivity.

As used herein, the term “metal” means those elements that are in thed-block and f-block of the Periodic Chart of the Elements, along withthose elements that have metal-like properties, such as silicon andgermanium. As used herein, the phrase “d-block” means those elementsthat have electrons filling the 3d, 4d, 5d, and 6d orbitals surroundingthe nucleus of the element. As used herein, the phrase “f-block” meansthose elements that have electrons filling the 4f and 5f orbitalssurrounding the nucleus of the element, including the lanthanides andthe actinides. Preferred metals include indium, silver, copper,aluminum, tin, bismuth, gallium and alloys thereof, silver coatedcopper, and silver coated aluminum. The term “metal” also includesalloys, metal/metal composites, metal ceramic composites, metal polymercomposites, as well as other metal composites. As used herein, the term“compound” means a substance with constant composition that can bebroken down into elements by chemical processes.

Of special efficacy is a filler comprising a particular form of carbonfiber referred to as “vapor grown carbon fiber” (VGCF), such as isavailable from Applied Sciences, Inc., Cedarville, Ohio. VGCF, or“carbon micro fibers”, are highly graphized types by heat treatment(thermal conductivity=1900 w/m° C.). Addition of about 0.5 wt. % carbonmicro fibers provides significantly increased thermal conductivity. Suchfibers are available in varying lengths and diameters; namely, 1millimeter (mm) to tens of centimeters (cm) length and from under 0.1 toover 100 μm in diameter. One useful form of VGCF has a diameter of notgreater than about 1 μm and a length of about 50 to 100 μm, and possessa thermal conductivity of about two or three times greater than withother common carbon fibers having diameters greater than 5 μm.

It is difficult to incorporate large amounts of VGCF in polymer systemsand interface components and systems, such as the hydrogenated rubberand resin combination already discussed. When carbon microfibers, e.g.(about 1 μm, or less) are added to the polymer they do not mix well,primarily because a large amount of fiber must be added to the polymerto obtain any significant beneficial improvement in thermalconductivity. However, we have discovered that relatively large amountsof carbon microfibers can be added to polymer systems that haverelatively large amounts of other conventional fillers. A greater amountof carbon microfibers can be added to the polymer when added with otherfibers, which can be added alone to the polymer, thus providing agreater benefit with respect to improving thermal conductivity of thethermal interface component. Desirably, the ratio of carbon microfibersto polymer is in the range of 0.05 to 0.50 by weight.

Optional materials may be added, such as catalysts, inhibitors and/orTheological modifiers. As used herein, the term “catalyst” means thatsubstance or condition that notably affects the rate of a chemicalreaction without itself being consumed or undergoing a chemical change.Catalysts may be inorganic, organic, or a combination of organic groupsand metal halides. Although they are not substances, light and heat canalso act as catalysts. In contemplated embodiments, the catalyst is anacid. In preferred embodiments, the catalyst is an organic acid, such ascarboxylic, acetic, formic, benzoic, salicylic, dicarboxylic, oxalic,phthalic, sebacic, adipic, oleic, palmitic, stearic, phenylstearic,amino acids and sulfonic acid. Antioxidants may also be added to inhibitoxidation and thermal degradation of the cured rubber gel or solidthermal interface component. Typical useful antioxidants include Irganox1076, a phenol type or Irganox 565, an amine type, (at 0.01% to about 1wt. %), available from Ciba Giegy of Hawthorne, N.Y. Typical cureaccelerators include tertiary amines such as didecylanethylamine, (at 50ppm—0.5 wt. %).

One or more solvents may also be added to the thermal interfacematerials and/or coating compositions in order to modify the physicaland/or chemical properties of the materials. Contemplated solventsinclude any suitable pure or mixture of organic or inorganic moleculesthat are volatilized at a desired temperature and/or easily solvates thethermal interface materials and/or coating compositions. The solvent mayalso comprise any suitable pure or mixture of polar and non-polarcompounds. In some embodiments, the solvent comprises benzene,trichloroethylene, toluene, ethers, cyclohexanone, butryolactone,methylethylketone, and anisole. As used herein, the term “pure” means iscomposed of a single molecule or compound. For example, pure water iscomposed solely of H₂O. As used herein, the term “mixture” means thatcomponent that is not pure, including salt water. As used herein, theterm “polar” means that characteristic of a molecule or compound thatcreates an unequal charge, partial charge or spontaneous chargedistribution at one point of or along the molecule or compound. As usedherein, the term “non-polar” means that characteristic of a molecule orcompound that creates an equal charge, partial charge or spontaneouscharge distribution at one point of or along the molecule or compound.

In some contemplated embodiments, the solvent or solvent mixture(comprising at least two solvents) comprises those solvents that areconsidered part of the hydrocarbon family of solvents. Hydrocarbonsolvents are those solvents that comprise carbon and hydrogen. It shouldbe understood that a majority of hydrocarbon solvents are non-polar;however, there are a few hydrocarbon solvents that could be consideredpolar. Hydrocarbon solvents are generally broken down into threeclasses: aliphatic, cyclic and aromatic. Aliphatic hydrocarbon solventsmay comprise both straight-chain compounds and compounds that arebranched and possibly crosslinked, however, aliphatic hydrocarbonsolvents are not considered cyclic. Cyclic hydrocarbon solvents arethose solvents that comprise at least three carbon atoms oriented in aring structure with properties similar to aliphatic hydrocarbonsolvents. Aromatic hydrocarbon solvents are those solvents that comprisegenerally three or more unsaturated bonds with a single ring or multiplerings attached by a common bond and/or multiple rings fused together.Contemplated hydrocarbon solvents include toluene, xylene, p-xylene,m-xylene, mesitylene, solvent naphtha H, solvent naphtha A, alkanes,such as pentane, hexane, isohexane, heptane, nonane, octane, dodecane,2-methylbutane, hexadecane, tridecane, pentadecane, cyclopentane,2,2,4-trimethylpentane, petroleum ethers, halogenated hydrocarbons, suchas chlorinated hydrocarbons, nitrated hydrocarbons, benzene,1,2-dimethylbenzene, 1,2,4-trimethylbenzene, mineral spirits, kerosine,isobutylbenzene, methylnaphthalene, ethyltoluene, ligroine. Particularlycontemplated solvents include, but are not limited to, pentane, hexane,heptane, cyclohexane, benzene, toluene, xylene and mixtures orcombinations thereof.

In other contemplated embodiments, the solvent or solvent mixture maycomprise those solvents that are not considered part of the hydrocarbonsolvent family of compounds, such as ketones, such as acetone, diethylketone, methyl ethyl ketone and the like, alcohols, esters, ethers andamines. In yet other contemplated embodiments, the solvent or solventmixture may comprise a combination of any of the solvents mentionedherein.

The coating material is designed to laminate any surface, substrate orsurface area that comprises a thermal interface material or othersuitable material that may contaminate additional layers with componentsand/or debris of the thermal interface material or composition. Acontemplated thermal interface material comprises GELVET®.

GELVET®, as mentioned, is a compliant fibrous interface component thatcomprises a plurality of thermally conductive fibers, an encapsulant andan optional adhesive material. Examples of compliant fibrous interfacecomponents can be found in U.S. patent application Ser. No. 09/193,415;U.S. patent application Ser. No. 09/103,416 and U.S. patent applicationSer. No. 09/333,564, and PCT Application Serial No. PCT/US02/17331 filedon May 30, 2002—all of which are commonly owned and incorporated hereinby reference in their entirety. GELVET® comprises a thermal conductivityof about 30.0 W/mK, a thermal resistance of about 0.68° C.cm²/W (0.0010°C.cm²/W), is typically applied at a thickness of about 0.012 to 0.100inches (0.3-2.5 mm) and comprises a typical softness of about greaterthan 25% of deflection under 10 psi. Typical characteristics of GELVET®are a) thickness variable over a wide range, b) compliance to geometricand thermal mismatch, c) very high thermal conductivity, and d) reliableover long-term use of the component.

Suitable thermally conductive fibers comprise diamond fibers, conductivepolymer fibers, carbon fibers, graphite fibers and metal fibers, such ascopper fibers and aluminum fibers. The thermally conductive fibers arecut to a particular length, e.g. from at least about 0.0005 inches to atleast about 1 inch. Thermally conductive fibers contemplated herein mayalso be cut to at least about 0.001 inches, to at least about 0.01inches and/or to at least about 0.1 inches. Thermally conductive fiberscontemplated herein may have a fiber diameter of at least about 3microns, of at least about 30 microns and/or at least about 300 microns.Conductive fibers having a fiber diameter of at least about 10 micronsare presently preferred. Suitable thermally conductive fibers have athermal conductivity of at least about 25 W/mK. Some suitable fibers arethose available from Amoco identified as K-1100, K-800, P-120, P-100,P-70 and T50; as well as fibers available from Toray designated as M46Jand M46JB.

Thermally conductive fibers disclosed herein can be cleaned, ifnecessary, to remove any coatings present on the fibers. Somecommercially available fibers are sold with a coating applied to thesurface, which is preferably removed by cleaning the fibers. One methodof cleaning thermally conductive fibers is by heating the fibers in airto burn off the coating, i.e. sizing. However, chemical cleaning methodscan also be used.

Substrates and surfaces contemplated herein may comprise any desirablesubstantially solid material. Particularly desirable substrate layerswould comprise films, glass, ceramic, plastic, metal or coated metal, orcomposite material. In preferred embodiments, the substrate comprises asilicon or germanium arsenide die or wafer surface, a packaging surfacesuch as found in a copper, silver, nickel or gold plated leadframe, acopper surface such as found in a circuit board or package interconnecttrace, a via-wall or stiffener interface (“copper” includesconsiderations of bare copper and it's oxides), a polymer-basedpackaging or board interface such as found in a polyimide-based flexpackage, lead or other metal alloy solder ball surface, glass andpolymers such as polymimide. The “substrate” may even be defined asanother polymer material when considering cohesive interfaces. In morepreferred embodiments, the substrate comprises a material common in thepackaging and circuit board industries such as silicon, copper, glass,and another polymer.

As mentioned, a method of forming a thermal interface material isdisclosed herein that includes: a) providing at least two siloxane-basedcompounds; b) providing at least one inorganic micro-filler material; c)providing at least one thermally conductive filler material; and d)combining the at least two siloxane-based compounds, the at least oneinorganic micro-filler material and the at least one thermallyconductive filler material. It is contemplated that the steps ofproviding at least two siloxane-based compounds, at least one inorganicmicro-filler material and at least one thermally conductive fillermaterial can be achieved by a) buying these materials from a supplier;b) preparing or producing the these materials in house using chemicalsprovided by another source and/or c) preparing or producing thesematerials in house using chemicals also produced or provided in house orat the location.

In a contemplated embodiment, GELVET® is coated with a top coating sothat any loose fiber debris can be mechanically blocked from the topsurface, while simultaneously locking oil migration, without sacrificingthermal performance. The challenge of this approach comes from siliconebase of GELVET®. As mentioned earlier, silicone has some intrinsicproperties such as very low surface energy and a low coefficient ofthermal expansion (CTE) compared with various polymers. These propertiesimply that the choice of coating material is limited to the one whichhas a similar silicone structure, otherwise delamination resulting frompoor adhesion between silicone base and top coating and CTE mismatchwill inevitably take place during burn-in process. However, siliconebased coating cannot efficiently block oil migration from the thermalinterface materials and itself in fact is a source of new oilcontamination.

The thermally conductive coating composition can be applied on thethermal interface by an automatic screen printer and then heat cured.However, any suitable application process or method, such as ink jetprinting, rolling, dripping, and spinning on, and any suitable curingmethod using extended or point sources, such as light sources, lasersources, and IR sources, may also be used. After applying thecomposition, the interface is installed onto the burn-in socket with thetest chip. After five times high-speed actuation followed by 150° C. for20 hours of high temperature baking, the test chip revealed a cleansurface without any oil and fiber debris contamination.

Once the thermal interface materials and/or coating compositions areapplied, additional layers or components may be added to the sealedmaterial. It is contemplated that the additional layers will comprisematerials similar to those already described herein, including metals,metal alloys, composite materials, polymers, monomers, organiccompounds, inorganic compounds, organometallic compounds, resins,adhesives and optical wave-guide materials.

A layer of laminating material or cladding material can be coupled tothe layered interface materials depending on the specifications requiredby the component. Laminates are generally considered fiber-reinforcedresin dielectric materials. Cladding materials are a subset of laminatesthat are produced when metals and other materials, such as copper, areincorporated into the laminates. (Harper, Charles A., ElectronicPackaging and Interconnection Handbook, Second Edition, McGraw-Hill (NewYork), 1997.)

Spin-on layers and materials may also be added to the layered interfacematerials or subsequent layers. Spin-on stacked films are taught byMichael E. Thomas, “Spin-On Stacked Films for Low k_(eff) Dielectrics”,Solid State Technology (July 2001), incorporated herein in its entiretyby reference.

Applications of the contemplated thermal interface components, layeredinterface materials and compliant fibrous interface components describedherein comprise incorporating the materials and/or components intoanother layered material, an electronic component or a finishedelectronic product. Electronic components, as contemplated herein, aregenerally thought to comprise any layered component that can be utilizedin an electronic-based product. Contemplated electronic componentscomprise circuit boards, chip packaging, separator sheets, dielectriccomponents of circuit boards, printed-wiring boards, and othercomponents of circuit boards, such as capacitors, inductors, andresistors.

Electronic-based products can be “finished” in the sense that they areready to be used in industry or by other consumers. Examples of finishedconsumer products are a television, a computer, a cell phone, a pager, apalm-type organizer, a portable radio, a car stereo, and a remotecontrol. Also contemplated are “intermediate” products such as circuitboards, chip packaging, and keyboards that are potentially utilized infinished products.

Electronic products may also comprise a prototype component, at anystage of development from conceptual model to final scale-up/mock-up. Aprototype may or may not contain all of the actual components intendedin a finished product, and a prototype may have some components that areconstructed out of composite material in order to negate their initialeffects on other components while being initially tested.

Generally, the concept and method of this invention is not limited toGELVET® material, but it is applicable on any silicone-based materialsor those materials, which have any oil contamination concerns. So thethermal interface materials and/or coating compositions disclosed hereinnot only solved the problem of existing TIM products, but also creates aplatform technology for future innovations. Furthermore, as discussedearlier, the thermal interface materials and/or coating compositionsdisclosed herein a) have a low thermal resistance; b) are relativelyfree of oil contamination; c) make good coating compositions; and d)make self-assembled physical barriers or interfaces between theunderlying thermal interface material and additional components.

EXAMPLES

In accordance with the present invention, the thermally conductivecoating composition can be made and used as illustrated, by followingpreferred embodiments: Exp. 1 Exp. 2 Exp. 3 Exp. 4 Exp. 5 Exp. 6 PART AVinyl terminated 30-50% 30-50% 30-50% 30-50% 30-50% 30-50%polydimethylsiloxane Platinum catalyst solution 0.05-0.5%  0.05-0.5% 0.05-0.5%  0.05-0.5%  0.05-0.5%  0.05-0.5%  silicon dioxide flake  5-20% 5-20%  5-20%  5-20%  5-20%  5-20% Boron Nitride 10-50%  5-20% 10-50%10-50% 10-50% Copper powder 10-50% Silica powder 25-60%Eeonomer(conductive polymer 0.1-0.5% 0.1-0.5% 0.1-0.5% 0.1-0.5% 0.1-0.5%0.1-0.5% filler) PART B Vinyl terminated 60-90% 60-90% 60-90%polydimethylsiloxane Dimethylsiloxane-  5-20%  5-20%  5-20%methylhydrosiloxane copolymer Vinylmethylcyclotetrasiloxane 0.1-1%  0.1-1%   0.1-1%   Polytetradecylmethylsiloxane  1-10%  1-10%  1-10%Polyoctylmethylsiloxane  1-10% Decylmethylsiloxane/butylated  1-10%aryloxy-propylmethylsiloxane Octadecylmethylsiloxane/  1-10%dimethylsiloxane

The components of Part A were weighted and mixed in a Hobart mixer forabout 10 min. to form a dough and then further processed by a three-rollmixer for three passes and degassed in a planetary mixer under the fullvacuum (≦−98 Kpa) for about 20 min. The components of Part B wereweighted and mixed in a planetary mixer under the full vacuum (≦−98 Kpa)for about 20 min. The components can then be stored at room temperatureuntil blending before use. The coating composition is obtained byblending Part A with Part B in a ratio of 4:1 by weight in a planetarymixer under the full vacuum (<−98 Kpa) for about 10 min. The compositionis then stored in a −40C freezer.

At this point it should be understood that, unless otherwise indicated,all numbers expressing quantities of ingredients, constituents, reactionconditions and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the subject matter presented herein. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the subject matter presented herein are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

The coating composition is applied on to the GELVET® surface by anautomatic screen printer or appropriate methods. The composition isfirst thawed at room temperature for about 15 min after removing fromthe freezer and laminated on the top surface of the TIM using 1.7mil-opening screen, then vacuumed for seven minutes. The coated GELVET®is then cured in a 150° C. box oven for about 60 min. For the othersilicone based thermal interface materials, the said coating compositioncan be stencil (thickness less than 0.5 mil) printed on the top surface,vacuumed and then oven cured for about 60 min at 150° C.

Thus, specific embodiments and applications of thermally conductivecoating compositions have been disclosed. It should be apparent,however, to those skilled in the art that many more modificationsbesides those already described are possible without departing from theinventive concepts herein. The inventive subject matter, therefore, isnot to be restricted except in the spirit of the appended claims.Moreover, in interpreting both the specification and the claims, allterms should be interpreted in the broadest possible manner consistentwith the context. In particular, the terms “comprises” and “comprising”should be interpreted as referring to elements, components, or steps ina non-exclusive manner, indicating that the referenced elements,components, or steps may be present, or utilized, or combined with otherelements, components, or steps that are not expressly referenced.

1. A thermal interface composition, comprising: at least twosiloxane-based compounds, wherein each compound has a differentsolubility parameter, at least one inorganic micro-filler material, andat least one thermally conductive filler material.
 2. The thermalinterface composition of claim 1, wherein at least one of thesiloxane-based compounds comprises a polysiloxane compound.
 3. Thethermal interface composition of claim 1, wherein at least one of thesiloxane-based compounds comprises a hydride-functional siloxanecompound.
 4. The thermal interface composition of claim 2, wherein thepolysiloxane compound comprises a substituted polysiloxane compound. 5.The thermal interface composition of claim 4, wherein the polysiloxanecompound is substituted by a functional group comprising an alkyl group,an aromatic group, a halide group or a combination thereof.
 6. Thethermal interface composition of claim 4, wherein the substitutedpolysiloxane compound comprises an alkenyl-terminated polyalkylsiloxane.7. The thermal interface composition of claim 6, wherein thealkenyl-terminated polyalkylsiloxane comprises a vinyl group.
 8. Thethermal interface composition of claim 7, wherein the alkenyl-terminatedpolyalkylsiloxane further comprises a methyl group.
 9. The thermalinterface composition of claim 5, wherein the polysiloxane compoundcomprises vinylmethylcyclotetrasiloxane, polytetradecylmethylsiloxane,polyoctylmethylsiloxane, decylmethylsiloxane, butylatedaryloxy-propylmethylsiloxane, ctadecylmethylsiloxane, dimethylsiloxaneor a combination thereof.
 10. The thermal interface composition of claim3, wherein the hydride-functional siloxane comprisesmethylhydrosiloxane.
 11. The thermal interface composition of claim 1,wherein the inorganic micro-filler material comprises silicon dioxide.12. The thermal interface composition of claim 1, wherein the inorganicmicro-filler material comprises a powder.
 13. The thermal interfacecomposition of claim 1, wherein the inorganic micro-filler materialcomprises a flake.
 14. The thermal interface composition of claim 1,wherein the thermally conductive filler material comprises a transitionmetal.
 15. The thermal interface composition of claim 1, wherein thethermally conductive filler material comprises boron.
 16. The thermalinterface composition of claim 14, wherein the transition metalcomprises copper.
 17. The thermal interface composition of claim 15,wherein the thermally conductive filler material comprises boronnitride.
 18. The thermal interface material of claim 1, furthercomprising at least one additive.
 19. The thermal interface material ofclaim 18, wherein the additive comprises a catalyst.
 20. The thermalinterface material of claim 18, wherein the additive comprises aninhibitor.
 21. The thermal interface material of claim 18, wherein theadditive comprises a rheological modifier.
 22. The thermal interfacecomposition of claim 19, wherein the catalyst comprises platinum. 23.The thermal interface composition of claim 20, wherein the inhibitorcomprises an antioxidant.
 24. The thermal interface composition of claim21, wherein the Theological modifier comprises at least one solvent. 25.A coating composition comprising the thermal interface composition ofclaim
 1. 26. A coating composition comprising the thermal interfacecomposition of claim
 18. 27. An electronic component comprising thethermal interface composition of claim
 1. 28. An electronic componentcomprising the thermal interface composition of claim
 18. 29. Anelectronic component comprising the coating solution of claim
 25. 30. Anelectronic component comprising the coating solution of claim
 26. 31. Asemiconductor component comprising the thermal interface composition ofclaim
 1. 32. A semiconductor component comprising the thermal interfacecomposition of claim
 18. 33. A semiconductor component comprising thecoating solution of claim
 25. 34. A semiconductor component comprisingthe coating solution of claim
 26. 35. A method of forming a thermalinterface material, comprising: providing at least two siloxane-basedcompounds, wherein each compound has a different solubility parameter,providing at least one inorganic micro-filler material, providing atleast one thermally conductive filler material, and combining the atleast two siloxane-based compounds, the at least one inorganicmicro-filler material and the at least one thermally conductive fillermaterial.
 36. The method of claim 35, wherein at least one of thesiloxane-based compounds comprises a polysiloxane compound.
 37. Themethod of claim 35, wherein at least one of the siloxane-based compoundscomprises a hydride-functional siloxane compound.
 38. The method ofclaim 36, wherein the polysiloxane compound comprises a substitutedpolysiloxane compound.
 39. The method of claim 38, wherein thepolysiloxane compound is substituted by a functional group comprising analkyl group, an aromatic group, a halide group or a combination thereof.40. The method of claim 38, wherein the substituted polysiloxanecompound comprises an alkenyl-terminated polyalkylsiloxane.
 41. Themethod of claim 40, wherein the alkenyl-terminated polyalkylsiloxanecomprises a vinyl group.
 42. The method of claim 41, wherein thealkenyl-terminated polyalkylsiloxane further comprises a methyl group.43. The method of claim 39, wherein the polysiloxane compound comprisesvinylmethylcyclotetrasiloxane, polytetradecylmethylsiloxane,polyoctylmethylsiloxane, decylmethylsiloxane, butylatedaryloxy-propylmethylsiloxane, octadecylmethylsiloxane, dimethylsiloxaneor a combination thereof.
 44. The method of claim 37, wherein thehydride-functional siloxane comprises methylhydrosiloxane.
 45. Themethod of claim 35, wherein the inorganic micro-filler materialcomprises silicon dioxide.
 46. The method of claim 35, wherein theinorganic micro-filler material comprises a powder.
 47. The method ofclaim 35, wherein the inorganic micro-filler material comprises a flake.48. The method of claim 35, wherein the thermally conductive fillermaterial comprises a transition metal.
 49. The method of claim 35,wherein the thermally conductive filler material comprises boron. 50.The method of claim 48, wherein the transition metal comprises copper.51. The method of claim 49, wherein the thermally conductive fillermaterial comprises boron nitride.
 52. The method of claim 35, furthercomprising at least one additive.
 53. The method of claim 52, whereinthe additive comprises a catalyst.
 54. The method of claim 52, whereinthe additive comprises an inhibitor.
 55. The method of claim 52, whereinthe additive comprises a rheological modifier.
 56. The method of claim53, wherein the catalyst comprises platinum.
 57. The method of claim 54,wherein the inhibitor comprises an antioxidant.
 58. The method of claim55, wherein the rheological modifier comprises at least one solvent. 59.A coating composition produced from the method of claim
 35. 60. Acoating composition produced from the method of claim
 52. 61. Anelectronic component comprising the coating solution of claim
 59. 62. Anelectronic component comprising the coating solution of claim
 60. 63. Asemiconductor component comprising the coating solution of claim
 59. 64.A semiconductor component comprising the coating solution of claim 60.